Silver halide emulsions containing antiplumming and anti-bronzing agents



United States Patent SILVER HALIDE EMULSIONS CONTAINING ANTI- PLUNIMIN GAND ANTI-BRONZING AGENTS Norman E. Parnell, East Brunswick Township,Middlesex County, N. J., assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware No Drawing.Application December 19, 1952, Serial No. 327,049

18 Claims. (Cl. 95-7) This invention relates to photographic silverhalide emulsions and emulsion layers which have improved resistance toplumming and bronzing of developed images in photographic elementsembodying such emulsions and to processes of making the same. Moreparticularly, it relates to such emulsions and emulsion layerscontaining finely divided particles of an antiplumming agent suspendedin wax particles.

This invention has for an objective the provision of improvedphotographic elements and particularly photographic papers. Anotherobject is to improve the quality of the finished photographic imageobtained when prints are dried upon hot ferrotype equipment. A furtherobject is to provide photographic silver halide layers which areresistant to the phenomenon known as plumming, or bronzing, which occurson hot ferrotyping photographic prints and is characterized by theformation of poor image color and a decrease in image density. Anadditional object is to improve the effectiveness of antiplumming agentsin photographic silver halide emulsion layers. Still another object isthe provision of plummingresistant photographic materials in whichspeed-loss and contrast-increase, encountered when employing anantiplumrning agent as an emulsion adjuvant, are minimized. Otherobjects will be apparent from the following description of theinvention.

The above objects are attained and new and useful photographic emulsionsand emulsion layers are obtained by bringing into intimate mixture withthe lightsensitive silver halide grains or an aqueous dispersionthereof, in a water-permeable colloid, finely divided particles of a waxcontaining an anti-plumming agent. The particles of the latter agent areprovided with a thin skin or coating, the thickness of which varies inaccordance with the proportion of wax to agent. This coating effectivelyprevents the anti-plumming agent from acting upon the photosensitivesilver halides during storage and treatment of the exposed photographicelement in aqueous processing baths, but releases the agent when thephotographic element is placed in contact with the hot ferrotype plate.7 I

Various natural and synthetic waxes can be used for this purposeincluding mineral waxes, vegetable waxes, animal waxes, etc., includingsoft, hard and microcrystalline paraffin waxes; ozokerite, ceresin,carnauba wax, beeswax, montan wax, synthetic waxes, e. g., seekay waxobtained by chlorinating naphthalene, chlorinated biphenyl, higheraliphatic cyanides or nitriles, higher aliphatic acid amides, methylenedistearamide, ethylene disteararnide and the corresponding bis amidesfrom lauric, palmitic and oleic acid and mixtures of two or more of suchamides, the synthetic wax sold under the trade name Ceramid by 'GlycoProducts Co., Inc., New York, etc. The useful waxes, in general, shouldbe solid at 25 C. and melt at the temperature used for the hot ferrotypeplate, e. g., below l00 C. The parafiin waxes are preferred.

The'above waxes are-jwater-insoluble and-are not 2,726,955 Patented Dec.13, 1955 ICC affected by the alkaline materials or acid materialspresent in the usual developing, fixing and stop baths used inprocessing exposed photographic papers to photographic images orpictures.

In general, the procedure for inertizating an antiplummiug agentconsists of incorporating the anti-plumrning agent in the molten wax. Ifthe anti-plumming compound is soluble in the wax or resin, a solutionmay be prepared; otherwise, it is necessary to form a solution using acommon solvent, or a colloidal suspension with a suitable dispersingagent. In the case of 1-phenyl- S-mercaptotetrazole and relatedl-hydrocarbon-substituted S-mercaptotetrazoles and methylene stearamide,for example, it is possible to dissolve the anti-plurnming agentdirectly in the liquefied wax. By melting paraffin Wax and coolingcarefully it is possible to disperse finely divided particles ofl-phenyl-5-mercaptottetrazole, which is insoluble in paraflin wax,directly in the wax. However, dispersing agents, e. g., sodiump-tertiaryoctyiphenoxyethoxyethyl sulfonate, aid in securing stablesuspensions. The Wax solution or dispersion may be dispersed in turn inWater, which may contain dispersing agents, a water-permeable colloid,e. g., gelatin, forming a suspension of Wax particles in which theanti-plumming agent particles are coated. The Water dispersion is thenadded to a silver halide photographic emulsion in the desired amount,coated on a suitable support, and air dried. These coatings, afterreceiving a standard exposure through a standard negative, are processedin the appropiate developer, acid stop and fixing solutions. The printsobtained when dried upon a hot ferrotype plate are essentally free fromplumming and exhibit no loss in density, and no appreciable change inemulsion speed and contrast.

The preparation of the water dispersion of the resin solution or initialwax dispersion should be performed in a manner that will minimizeleaching of the anti-plumming compound from the protective coating ofwax. The use of water-insoluble solvents which have a high solventaction upon the anti-plumming agent, compared to the solubility inwater, is advantageous, although satisfactory coating With theanti-plumming agent or inertization is possible with certainwater-soluble solvents. Coating of the agent is usually aided byconcentrating the wax and anti-plurnming agent in the same solventphase. The choice of a solvent using the solute distribution laws ofmultiphase systems as a guiding principle tending from thesubmicroscopic to approximately 30 microns in diameter.

In dispersing the mixture of Wax and antiplumming agent directly in anaqueous colloid solution or aqueous colloid silver halide dispersion onemay use small amounts of a dispersing agent. Suitable dispersing agentsinclude sodium and potassium alkyl sulfates of 10 to 18 carbon atoms,sodium alkylsulfonates of 10 to 18 carbon atoms, polyoxyethylene ethersof ring-dehydration products of a hexitol (see U. S. Patent 2,400,532),sorbitan monosterate, etc. Good dispersion can be made without agents.

While it is preferable to disperse the wax-coated particles of theanti-plumrning agent in the colloid-silver halide dispersion theinvention is not limited to this embodiment. ..Good.resnlts can..beobtained by. coating a layer of a water-permeable colloid containing thecoated anti-plumming agent directly onto a colloid silver halideemulsion layer or by bathing such an emulsion layer with a dispersion ofthe wax-protected anti-plumming agent.

The invention will be further illustrated but is not intended to belimited by the following examples.

EXAMPLE I First, a suspension of finely-divided particles ofl-phenyl--mercaptotetrazole, having a particle size of not more than 30microns in their largest diameter, in paraffin Wax was formed by melting200 grams of the Wax, adding 2 grams of sodiump-tertiary-octylphenoxyethoxyethyl sulfonate as a dispersant and thenincorporating 20 grams of the l-pheuyl-S-mercaptotetrazole. By coolingslowly with good agitation, a dispersion of l-phenyl-S-mercaptotetrazolein the solid Wax was obtaine Next, a solution consisting of 5 grams ofthe polyoxyethylene ether of dodecyl alcohol in 150 ml. of distilledwater was prepared and added to a high-speed liquid mixer of the typedescribed in Osius U. S. Patent 2,109,501. A 4-gram portion of thesuspension of wax-protected l-phenyl-S-mercaptotetrazole particles wasthen added and vigorously agitated for five minutes.

A chloro-bromide emulsion (AgCl=95.2 mole per cent, and AgBr=4.8 moleper cent) was prepared by a procedure which normally yields a standardcontact printing speed emulsion. Immediately before coating thisemulsion upon a baryta coated paper support, 50 ml. of the wax-protectedl-phenyl-S-mercaptotetrazole dispersion was added to a quantity ofemulsion having a silver content equivalent to that contained in 12.5ml. of 3 N silver nitrate solution at 25 C. In all other respects theprocedures for preparation and coating of contact printing paper typeemulsion were followed. Control coatings were made at the same time withportions of the original emulsion, which included no1-phenyl-5-mercaptotetrazole in one case, and the above wax-protectedl-phenyl-S-metcaptotetrazole in a second case. The coatings were dried,and samples cut and exposed to a standard negative in the standardtesting set-up for contact type emulsion to obtain matched prints. Allprints were developed for one minute at 20 C. in developer made bydiluting 1 part of the following stock solution:

Water ml 500 Metol g ams" 3.0 Sodium sulfite (anhydrous) do 45.0Hydroquinone do 12.0 Sodium carbonate (anhydrous) do 67.5 Potasiumbromide do.. 1.9

Water to make 1.0 liter. with 2 parts of water, rinsed in water, and.fixed in the following fixer solution:

Water ml 850 Sodium thiosulfate "grams-.. 240 Sodium sulfite (anhydrous)....do 15.0 Acetic acid (28%) ml 48.0 Boric acid (crystals) grams 7.5Potassium alum do 15.0

Add water to make 1.0 literfor five minutes. Processed prints from eachcoating were dried on a hot ferrotype plate, a cold ferrotype plate, andon a cheesecloth type screen to evaluate plumming. The results aretabulated as follows:

EXAMPLE n Initially, a dispersion of finely-divided particles of1-phenyl-S-mercaptotetrazole protected with paraflin wax having amelting point of 60 C. was prepared by melting 20 grams of the wax,adding 0.5 gram of an oxidized fatty acid of 12 to 20 carbon atoms as adispersing agent, and then slowly mixing in 2 grams of the anti-plummingcompound. Upon cooling slowly with good agitation, a suspension of the1-phenyl-5-mercaptotetrazole in the solid wax was formed. A 3-gramportion of this mixture was then added to a solution of 6 grams ofpolyoxyethylene sorbitan monolaurate (Tween 61 sold by Atlas Powder Co.)in ml. of distilled water contained in a high speed mixer of the typedescribed in U. S. Patent 2,109,501 and blended for three minutes. Thedispersion thus obtained was dilutedto 200 ml. and passed through acolloid mill three times, using a clearance settingof 0.002 inch and aspeed of 12,000 R. P. M. The dispersion thus obtained was tested in thesame manner as that described in Example 'I. A summary of the results ispresented in Table II.

A solution containing 4 grams of l-phenyl-S-mercaptotetrazole dissolvedin 36 grams of molten, synthetic wax having a melting point of 795 to805 C. and comprising a mixture of the amides prepared by reactingstearic acid with stearyl amines was prepared initially. Next, to 100ml. of distilled water in a high speed mixer as described in Example II,6 grams of sorbitan tristearate polyoxyethylene ether (Span 65 sold byAtlas Powder Co.) were added and blended for 30 seconds. Then, 3 gramsof the first molten solution were added and blended for three minutes.The resultant dispersion was diluted to 200 mLand passed through acolloid mill three successive times, the colloid ,mill being set for0.002 inch clearance and 12,000 R. P. M. The dispersion obtained wasevaluated in the manner given in Example I. The pertinent results arepresented in Table Table III Grams l-phenyl-e gelative P] d Cow mercapoxposure umme on Emulsmn tetrazole, Time Hot Ferrd? g per emul- (see) esion unit Control None Trace 20 Yes 2.0 Modifiedwith--. 1.360 None.. 33Moderately 3.0

less than control. Modified with 0.720 ---do. Siight1y 2.0

wax+.

Similar results can .be obtained with ether N-alkyl stearamidesincluding those made from interaction of lauric, palmitic, oleic, andstearic acids and mixtures of two or more thereof, with thecorresponding monoamines, i. e., dodecyl, etc., and mixed amines.

' EXAMPLE IV A .solution wasepreparedsby dissolving 2 grams ofl-phenyl-S-mercaptotetrazole in 20 grams of the molten synthetic waxdescribed in Example III. Next, a mixture of 4 grams of polyoxyethylenesorbitan monolaurate (Tween 61 sold by Atlas Powder Co.) in 100 ml. ofdistilled water was prepared and blended for 30 seconds in a high-speedmixer (U. S. P. 2,101,501). A 4-gram portion of the solidwax-1-pheny1-5-mercaptotetrazole solution was crushed and added with themixer in motion. Blending was continued for approximately three minutes.The resultant dispersion was tested as outlined in Ex- First, a solutioncomposed of 0.75 gram of l-phenyl- S-mercaptotetrazole dissolved in 7.5grams of molten stearyl stearamide was prepared and allowed to solidify.A Z-grarn portion of this solid solution was then added to 100 ml. ofdistilled water containing 5 grams of sorbitan monolaurate and 0.5 gramof cetyl-trimethylammonium bromide as a dispersant, and blended forthree minutes in a high-speed mixer (U. S. P. 2,109,501). The resultantsuspension was diluted to 150 ml. and passed through a colloid mill setfor 0.002 inch clearance and 12,000 R. P. M. After milling, distilledwater was used to rinse the emulsifying equipment and adjust the totalvolume to 250 ml. Results of the emulsion evaluation of the suspensoidobtained are tabulated in the following A second dispersion was madefollowing the procedure given in Example I, except that (Tween 81) wassubstituted for sodium p-tertiary-octylphenoxyethoxyethyl sulfonate.This dispersion was tested along with the first, so that the controlsare the same. The results are also given in Table V.

In the foregoing tables an emulsion unit is defined as that quantity ofemulsion having a silver content equivalent to that of 500 ml. of 3 NAgNOa at 25 C.

The contrast grade in the foregoing tables was determined visually bycomparing a print made in the standard manner with the scale of papercontrast grades used by E. I. du Pont de Nemours and Company in theircontrol laboratory at Rochester, New York, to grade photographic paperproducts for trade purposes.

The above examples evidence that by coating antiplumming agent particleswith a wax one can materially reduce the degree of plumming. Moreover,the quantity of the anti-plumming agent required to give effectiveantiplumming may be reduced by providing such a coating.

The invention is, of course, not limited to the use of the particularanti-plumming agent given in the foregoing examples as many other ofsuch agents can be used with like results. Among the additional usefulagents are the l-alkyl, l-aryl and l-cycloalkyl-5-mercaptotetrazoles, e.g., l-u-naphthyl-5-mercaptotetrazole, l-cyclohexyl-5-mercaptotetrazole,1-methyl-S-mercaptotetrazole, l-ethyl-S-mercaptotetrazole;S:S'-methylene-bis-thiuronium iodide, S:S'- ethylene-bis-thiuroniumbromide, S:S'-trimethylene-bisthiuronium bromide;2:2'-methylenethio-bis-dihydroiminazole dihydroiodide,2:2'-ethylenethio-bis-dihydroiminazole dihydrobromide,2:2trimethylenethio-bis-dihydro iminazole dihydrobromide,2:2'-ethylenethio-bis-(4-methyldihydroiminazole) dihydrobromide,2:2'-trimethylenethio-bis-(4-methyliminazole) dihydrobromide, disodium-2:2 ethylenethio bis (4-amino-6-hydroxypyrimidine),S:S'ethylene-bis-N-ethyl-thiuronium bromide,S:S-ethylene-bis-N:N-diethylthiuronium bromide, S:S'-trimethylene-bis-N:N"-triethylthiuronium bromide,S:S'-ethylenebis-N:N"-triethylthiuronium bromide,S:S-o-xylylenylbis-thiuronium bromide,S:S'-ethylenethio-bis-(l-methyldihydroiminazole)di p toluenesulfonate,S:S'-ethylene bis-N-phenyl-N-methylthiuronium bromide, 4:4-ethylenethio-bis-(4: 6-dithio-1 :3 5-thio diazine,2:2'-ethylenethiobis-(S-thiol-l 3 4-thiodiazole), S-ethylthiuroniumbromide, S-n-butylthiuronium bromide, S-cetyl thiuronium iodide,S-amidoethylthiuronium chloride, S-Z-thiazylamidomethylthiuroniumchloride and S-Z-pyridylamidomethylthiuronium chloride, etc. Mixtures oftwo or more of the anti-plumming agents can be used. They may be usedwith the waxes described above or mixtures of two or more of such waxes.

The proportion of anti-plumming agent to wax may vary from 1 to 25 partsby weight of the former per part by weight of the latter. The optimumamounts will vary with the particular agent and wax. When theanti-plumming agent also has good anti-fogging properties it is best tokeep the proportion of agent to wax in the higher portion of the aboverange.

Since waxes are insoluble in the pH ranges of the ordinary developingand fixing solutions the agents are essentially insolubilized orprotected by the wax coating during aqueous processing of a photographicpaper bearing an emulsion containing a wax-protected agent. The amountof free or exposed anti-plumming agent can be controlled to some extentby other factors among which are proper choice of solvents,concentrations, temperature, and the severity and time of application ofthe shearmg forces due to the dispersing equipment. It is also possibleto use hydrophilic colloid, e. g., gelatin solutions as the dispersionmedia, so that photographic emulsion Wash technique may be used toremove non-protected particles, which are water-soluble. Theanti-plumming agent is released by the heat of the hot ferrotype plate,which melts the protective Wax or resin coating.

The invention is not limited to gelatin silver halide emulsion andemulsion layers as many other water-permeable colloids can be used asthe binding agent for the silver halide grains with like results. Amongthe additional useful materials are agar agar, alginic acid, sodiumalginate, polyvinyl alcohol and its ethers and acetals including thecolor-former acetals of Jennings et al. U. S. P. 2,397,864, celluloseethers, etc. partially hydrolyzed esters of cellulose, etc.

While the invention is particularly useful with photographic printingpapers the support is not limited to paper but can be a cellulosederivative, e. g., cellulose acetate, cellulose nitrate, etc., a superpolymer, e. g., nylon, poly: vinyl chloride, polyethylene terephthalate,etc. These supports may conatin an opacifying agent or bear a coatingcontaining such an agent so that the surface is lightreflecting and thesupport does not transmit light.

An advantage of this invention is that it provides a simple andelfective method of improving the anti-plumming effect of anti-plumrningagents. Another advantage is that it reduces the quantity ofanti-plumming agent necessary to produce an'adequate result. A furtheradvantage is that it reduces the leaching of anti-plumming agents fromwater-permeable colloid silver halide emulsion layers. A still furtheradvantage resides in the fact that the additional material involved,viz., the wax, is inexpensive. Yet another advantage is that the methodof making the emulsions is simple and does not involve expensiveapparatus.

As many .widely different embodiments of this invention can be madewithout departing from the spirit and scope thereof, it is otbeunderstood that the invention is not to be limited except as defined bythe claims.

'What is claimed is:

1. A colloid silver halide emulsion having dispersed therethroughparticles of a wax containing an agent taken fromthe group consisting ofanti-plumming and antibronzing agents,.said agents being sulfurandnitrogencontaining organic compounds having the property of preventingthe formation of bronze, to plum-colored silver images upon thehot-drying of developed silver photographic images.

2. A'water-permeable colloid silver halide emulsion layer having a waxin particulate form dispersed throughout such layer and having ananti-plumming agent, said agent being a sulfurand nitrogen-containingorganic compound having the property of preventing the formation ofbronzeto plum-colored silver images upon the hot drying of developedsilver photographic images contained in the wax particles.

3. A water-permeable colloid silver halide emulsion having dispersedtherethrough particles of wax containing an anti-plumming agent, saidagent being a sulfurand nitrogen-containing organic compound having theproperty of 'preventingthe formation of bronze. to plumcolored silverimages upon the hot drying of developed silver photographic images, saidparticles having an average diameter not greater than 30 microns andsaid wax being solid at temperatures of C. and melting at a temperaturenot greater than 100 C. i

4. A gelatino silver halide emulsion having dispersed therethroughparticles of wax containing an anti-plumming agent, said agent being asulfurand nitrogen-containing organic compound having the property ofpreventing the formation of bronzeto plum-colored silver images upon thehot drying of developed silver photographic images, said particleshaving an average diameter not' greater than microns and said Wax beingsolid at temperatures of 25 C. and melting at a temperature not greaterthan 100 'C.

5. A water-permeable colloid silver halide emulsionhaving dispersedtherethrough particles of wax containing an agent taken from the groupconsisting of antiplumming and anti-.bronzing agents, said agents beingsulfurand nitrogen-containing organic componnds'having the property ofpreventing the formation of bronzeto plum-colored silver images upon thehot-drying of developed silver photographic images, said particleshaving an average diameter not greater than 30 microns and said waxbeing solid at temperatures of 25 C. and melting at a temperature notgreater than 100 C., theproportion of said agent to wax varying from 1to 25 partsk, the proportion of anti-plumming agentto wax varying from ito 25 parts by weight of the former per 'part by weight of the latter.

7. A water pe'rmeable colloid silver halide emulsion having dispersedtherethrough particles of a water-insoluble Wax containing al-hydro'c'arbon-S-rnercaptotetrazole.

8. A water-permeable colloid silver halide emulsion having dispersedtherethrough particles of a paraflin wax containing a1-hydrocarbon-5-mercaptotetrazole.

'9. A gelatino silver halide emulsion having therethrough particles ofparaffin wax containing l-phenyl-5 mercaptotetrazole.

10. A photographic element comprising a support hearing a colloid silverhalide emulsion layer wherein silver halide grains have in proximitytherewith particles of a wax containing an anti plumming agent, saidagent being a sulfurand nitrogen-containing organic compound having theproperty of preventing the formation of bronzeto plum-colored silverimages upon the hot drying of developed silver photographic images.

ll. An element as set forth in claim 10 wherein the wax particles aredistributed throughout the emulsion.

12. An element as set forth in claim 10 wherein the wax particles are ina separate water-permeable colloid layer disposed on the outer surfaceof the emulsion layer. 13. A photographic element comprising a papersupport bearing a waterrpermeable colloid silver halide emulsionlayerand having dispersed therethrough particles of a wax containing ananti-plumming agent, said agent being a sulfurand nitrogen-containingorganic compound havingthe property of preventing the formation ofbronzeto plum-colored silver images upon the hot drying of developedsilver photographic images.

14. A photographic element comprising a paper support bearing -awater-permeable silver halide emulsion layer having dispersedtherethrough particles of wax containing. an anti-plumming agent, saidagent being a sulfurandnitrogen-containing organic compound having theproperty of preventing the formation of bronzeto plum-colored silverimages upon the hot drying of developed silver photographic images, saidparticles having an average diameter not greaterthan 30 microns and saidwax being solid at temperatures of 25 C. and melting at a temperaturenot greater than 100 C.

'15. A photographic printing paper comprising a baryta coated papersheet bearing a gelatino silver halide emulsion having dispersedtherethrough particles of wax containing an anti-plumming agent, saidagent being a sulfurand nitrogen-containing organic compound having thecoated paper sheet bearing a gelatino silver halide emulsion havingdispersed therethrough particles of wax containing a1-hydrocarbon-S-mercaptotetrazole, said particles. having an averagediameter not greater than 30 microns andsaid wax being solid attemperatures of.

25 C. and melting at a temperature not greater than 17. Aphotographicprinting paper comprising a baryta coated paper sheetbearing a gelatino silver halide emul-.

1 sion having dispersed therethrough particles of wax containing al-phenyl-S-mercaptotetrazole, said particles having an average diameternot greater than 30 microns and said wax being solid at temperatures of2 5 C. and mel*- ing at a temperature notgreater than 100 C.

18. The process which comprises dispersing an antiplumming agent, saidagentlbeing a sulfurand nitrogencontaining organic compound having theproperty of preventing the formation of bronzeto plum-colored silverimages upon the hot drying: of developed silver photo- 9 graphic imagesin a wax and incorporating the wax-pro 2,221,873 tected particles ofsuch agent in a light-sensitive colloid 2,256,390 silver halideemulsion.

References Cited in the file of this patent 561,875

UNITED STATES PATENTS 2,059,829 Ward Nov. 3, 1936 10 Knoefel Nov. 19,1940 Hewitson Sept. 16, 1941 FOREIGN PATENTS Great Britain June 8, 1944

